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The Gravity Effect: an interview with Dr. Benjamin Levine

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Dr. Levine is the founder and director of the Institute for Exercise and Environmental Medicine (IEEM) at Texas Health Presbyterian Dallas. IEEM is the largest center for the study of human physiology in the United States. During the swim he will function as Ben’s cardiologist, as well as a researcher on two of The Longest Swim’s eight research projects.

The Longest Swim’s research partnerships extend well beyond the ocean- all the way into space! Bone demineralization, or a loss of bone density, is a health problem faced by astronauts during long-duration spaceflight. Finding ways to limit this damage is an important concern as a journey to Mars, estimated to take 6-8 months, comes closer to reality. Land-based research into the effects of low gravity can only eliminate one gravitational gradient: head-to-foot. Ben’s immersion in water will remove a second gradient, the front-to-back, making it a more ideal analogue to space travel. Although he will spend more time out of the water than in it, much of his time on the boat will be spent lying down (sleeping), so the amount of time Ben will spend upright during the 6 month journey is relatively small.

On the International Space Station bone demineralization is somewhat mitigated by weight-bearing exercise however the possible benefits of non-weight bearing exercise, which is what Ben will be doing as he swims, are unknown. Using a specialized x-ray technique, physicians will calculate the bone density of Ben’s body before and after the expedition. This approach allows scientists to evaluate both overall changes and any changes in density specific to a given bone region in his body.

Another issued faced by astronauts is vision loss, with symptoms similar to patients with high pressure in their brains. Unlike humans down on Earth, astronauts can never “stand up” while in space, which means they are unable to relieve pressure exerted on the back of the eye. Researchers are currently investigating if lowering this pressure while sleeping would be enough to address the problem. If Ben’s eye and optic nerve are in the same condition as they were before the Swim, and his visual acuity remains unchanged, that will be additional supporting evidence that their current approach will be effective for astronauts as well.

What makes Ben an ideal subject for this study?

Ben is going to do all his exercise supine, or prone (lying down). That’s especially interesting to me because in some ways it’s a model of long-duration spaceflight.

How so?

When you stand up gravity pulls blood into the feet and the heart becomes smaller and unloaded. When you’re lying down in the water, it’s actually a perfect model for spaceflight. And there’s one other interesting piece of information: when you’re upright on Earth there’s a lot of stress on your bones and muscles just from your body weight. In space all that goes away and astronauts lose bone mass over time. One of my colleagues, Dr. Adrian LeBlanc [at the Universities Space Research Association], is one of the world’s experts on the effect of spaceflight on the bones. When I told him about Ben’s study, he thought this was the perfect opportunity to look at whether exercise can prevent some of the bone loss we see in spaceflight.

And how can you learn that from a long-distance swimmer?

In the water you eliminate both the head-to-foot and front-to-back gravity gradient, so it’s as close a simulation of spaceflight as we can get on earth. We asked Ben to do a DXA scan [also called dual-energy x-ray absorptiometry or bone densitometry, DXA scans are today’s standard for measuring bone density] and looked at the bone density in his arms, back, and heels. After the swim, we’ll do another scan for comparison. What we want to see is if the exercise and increased blood flow from swimming protects Ben against any bone loss he might experience from long-duration weightlessness in the water.

Have you ever done this kind of study before?

We’ve actually done it on astronauts before and after they spent six months in space! So we’ll have a great comparison between them and Ben.

What about the effect of low gravity on your eyes?

We’ve noticed that some astronauts are losing their vision over a prolonged time in space and being in the prone position can raise the pressure within the eyes. Although, the water pressure balances that so we think that Ben will be fine in that respect.